Editing Geophysics (section)

=== Magnetism ===
{{further|Earth's magnetic field|Aeromagnetic survey|Paleomagnetism}}
The Earth's magnetic field protects the Earth from the deadly [[solar wind]] and has long been used for navigation. It originates in the fluid motions of the outer core.<ref name=Merrill/> The magnetic field in the upper atmosphere gives rise to the [[Aurora (astronomy)|auroras]].<ref name=Kivelson>{{harvnb|Kivelson|Russell|1995}}</ref>

[[Image:Geomagnetisme.svg|thumb|right|upright=1.1|Earth's dipole axis (pink line) is tilted away from the rotational axis (blue line). |alt=Diagram with field lines, axes and magnet lines.]][[File:Geodynamo Between Reversals.gif|thumb|left|Computer simulation of the [[Earth's magnetic field]] in a period of normal polarity between [[Geomagnetic reversal|reversals]]<ref>{{cite news |title=Earth's Inconstant Magnetic Field |url=https://science.nasa.gov/science-news/science-at-nasa/2003/29dec_magneticfield |access-date=13 November 2018 |work=science@nasa |publisher=National Aeronautics and Space Administration |date=29 December 2003 |language=en}}</ref>]]
The Earth's field is roughly like a tilted [[dipole]], but it changes over time (a phenomenon called geomagnetic secular variation). Mostly the [[geomagnetic pole]] stays near the [[geographic pole]], but at random intervals averaging 440,000 to a million years or so, the polarity of the Earth's field reverses. These [[geomagnetic reversals]], analyzed within a [[Geomagnetic reversal#Geomagnetic polarity time scale|Geomagnetic Polarity Time Scale]], contain 184 polarity intervals in the last 83 million years, with change in frequency over time, with the most recent brief complete reversal of the [[Laschamp event]] occurring 41,000 years ago during the [[Glacial period#Last glacial period|last glacial period]]. Geologists observed [[Geomagnetic reversal#History|geomagnetic reversal recorded]] in volcanic rocks, through [[Magnetostratigraphy#Correlation and ages|magnetostratigraphy correlation]] (see [[natural remanent magnetization]]) and their signature can be seen as parallel linear magnetic anomaly stripes on the seafloor. These stripes provide quantitative information on [[seafloor spreading]], a part of plate tectonics. They are the basis of [[magnetostratigraphy]], which correlates magnetic reversals with other [[Stratigraphic section|stratigraphies]] to construct geologic time scales.<ref name=Opdyke>{{harvnb|Opdyke|Channell|1996}}</ref> In addition, the [[paleomagnetism|magnetization in rocks]] can be used to measure the motion of continents.<ref name=Merrill/>